We live too far from eachother and have a big age difference what to do?

He is 20 and I'm 16. We know eachother for 5 months and have met one time , we have talked about things getting serious. The problem is we live too far from eachother he lives in America and I do too but I study in Germany so we wouldn't see often. I need advice on what to do cuz I'm starting to catch real feelings. I don't want to lose him. What should I do?